NHC Complexes of Group VI with Oxo and Nitrido ligands

The research project focusses on the development of new catalysts based on molybdenum and tungsten to deoxygenate oxidatively over-functionalized materials and biomass to convert them into valuable precursors useful for chemical industries. The aim is to abandon expensive late transition metals such as palladium or platinum from these processes and replace them with biocompatible and environmentally benign and cheap early transition metals. Furthermore, the conversion of nitrogen to ammonia and the direct incorporation of nitrogen into organic molecules will be probed to create value-added products. To reach these goals and to enhance the catalytic performance of molybdenum and tungsten in these processes a broad variety of new polydentate N-heterocyclic and mesoionic carbenes will be developed and the complexes reactivity will be evaluated. Modern spectroscopic techniques including multi-nuclear NMR spectroscopy, IR and UV-Vis spectroscopy, X-ray diffraction analysis and electrochemical methods will be used to gain new insights into the (electronic) structure of these materials. Combined with computational chemistry this will give us the possibility to in-depths evaluate the structures of the complexes proposed; a crucial knowledge to fully understand and tailor the demands necessary to develop further generations of active and robust catalysts.

The project investigated the applicability and use of N-heterocyclic and mesoionic carbene ligands in the chemistry of early transition metals, with a particular focus on molybdenum and tungsten. The results demonstrate that mesoionic carbenes, in particular, have a significant impact on the catalytic activity and stability of the metal complexes, thereby substantially enhancing their applicability. Overall, these findings lay an important foundation for the development of resource-efficient and environmentally friendly chemistry using biocompatible metals.